Semiconductor device with diode trench and schottky electrode

ABSTRACT

Provided is a semiconductor device that can be manufactured at low cost and that can reduce a reverse leak current, and a manufacturing method thereof. A semiconductor device has: a source region and a drain region having a body region therebetween; a source trench that reaches the body region, penetrating the source region; a body contact region formed at the bottom of the source trench; a source electrode embedded in the source trench; and a gate electrode that faces the body region. The semiconductor device also has: an n-type region for a diode; a diode trench formed reaching the n-type region for a diode; a p +  region for a diode that forms a pn junction with the n-type region for a diode at the bottom of the diode trench; and a schottky electrode that forms a schottky junction with the n-type region for a diode at side walls of the diode trench.

This application is a divisional application of a pending application,U.S. application Ser. No. 14/560,294 filed on Dec. 4, 2014, which is adivisional application of U.S. application Ser. No. 13/887,051 filed onMay 3, 2013, both of which are hereby incorporated by reference in theirentireties. This application claims the benefit of Japanese ApplicationNo. 2012-107673, filed in Japan on May 9, 2012, which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and amanufacturing method thereof.

2. Description of Related Art

The semiconductor device disclosed in Patent Document 1 includes aschottky barrier diode connected between the source and the drain. Morespecifically, in the semiconductor device, a p-type base layer is formedin the surface portion of an n-type semiconductor layer formed on ann-type semiconductor substrate. A trench is formed from the surface ofthe n-type semiconductor layer so as to penetrate the p-type base layer,and on the side walls and the bottom of the trench, a gate insulatingfilm is formed. A gate electrode is embedded in the trench. An n-typediffusion layer is formed in a surface portion of the p-type base layer.

With this configuration, this semiconductor device is equipped with atrench gate type transistor. In this transistor, the n-type diffusionlayer is a source region, the n-type semiconductor layer is a drainregion, and a channel is formed near the boundary between the gateinsulating film and the p-type base layer formed between the n-typediffusion layer and the n-type semiconductor layer. As a result, anelectric current flows between the source region and the drain region.

A metal layer is deposited on the surface of the n-type semiconductorlayer. The metal layer is in contact with the n-type diffusion layer,thereby functioning as a source electrode, and also, by the metal layerbeing in contact with the surface of the n-type semiconductor layer in aregion where the p-type base layer is not formed, a schottky junction isformed between the region and the metal layer. As described above, inthis semiconductor device, a transistor and a schottky barrier diode areformed in one chip.

RELATED ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Application Laid-Open Publication No.2009-59860

SUMMARY OF THE INVENTION

In manufacturing the semiconductor device of Patent Document 1, it isnecessary to form a protective film on the entire surface of the n-typesemiconductor layer before the trench for embedding the gate electrodetherein is formed. In this case, after forming the trench, it isnecessary to remove the protective film from a region where the schottkybarrier diode is to be formed. This makes the manufacturing process ofthe semiconductor device complex, and as a result, it becomes difficultto manufacture a semiconductor device at low cost.

Also, in order to improve the performance of the schottky barrier diode,a reduction in reverse leak current in a reverse bias state is soughtafter.

One of the objects of the present invention is to provide asemiconductor device that can be manufactured at low cost and that canreduce the reverse leak current, and a manufacturing method thereof.

Additional or separate features and advantages of the invention will beset forth in the descriptions that follow and in part will be apparentfrom the description, or may be learned by practice of the invention.The objectives and other advantages of the invention will be realizedand attained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, in thefirst aspect of the present invention, a semiconductor device has: asemiconductor layer of a first conductive type; a body region of asecond conductive type formed in the semiconductor layer of the firstconductive type; a source region and a drain region of the firstconductive type formed in the semiconductor layer so as to be separatedfrom each other across the body region; a source trench formed in thesemiconductor layer, the source trench penetrating the source region andreaching the body region; a body contact region formed near a bottom ofthe source trench and in the semiconductor layer of the first conductivetype that includes the body region, the body contact region being thesecond conductive type and having a higher impurity concentration thanthat of the body region; a source electrode embedded in the sourcetrench; a gate electrode facing through a gate insulating layer the bodyregion that lies between the source region and the drain region; a firstconductive type region for a diode formed in the semiconductor layer; adiode trench formed in the semiconductor layer that includes the firstconductive type region for a diode; a second conductive type region fora diode formed in the first conductive type region for a diode so as tobe in contact with a bottom of the diode trench, the second conductivetype region for a diode forming a pn junction with the first conductivetype region for a diode; and a schottky electrode forming a schottkyjunction with the first conductive type region for a diode at side wallsof the diode trench.

With this configuration, a transistor is formed in the semiconductorlayer outside of the diode forming region. In the diode forming region,a pn diode is formed at the bottom of the diode trench, and a schottkybarrier diode is formed at side walls of the diode trench. In this case,the source trench and the diode trench can be formed at the same time.Also, it is possible to form the body contact region at the bottom ofthe source trench at the same time as forming the second conductive typeregion for a diode at the bottom of the diode trench. Furthermore, it ispossible to embed the source electrode in the source trench at the sametime as forming the schottky electrode in the diode trench. In this way,the transistor and the diode can be formed at the same time, andtherefore, it is possible to omit a process that would be needed if thetransistor and the diode were formed in different processes (such as aprocess of forming a protective film on the surface of the semiconductorlayer and removing the protective film in the diode region after formingthe source trench). As described above, because the diode trench and thesecond conductive type region for a diode can be formed in the processfor forming the transistor (or in other words, because a special processfor forming the diode is no longer necessary), it is possible to form asemiconductor device that has a transistor and a schottky barrier diodeon the same chip with a smaller number of manufacturing steps. As aresult, the semiconductor device can be manufactured at low cost.

In a reverse bias state, a depletion layer spreads around the pn diodeat the bottom of the diode trench, which blocks the path of anelectrical current in the diode region, and as a result, the reverseleak current can be reduced.

In the second aspect of the present invention, the diode trench has thesame depth as that of the source trench. With this configuration, thediode trench and the source trench can be formed in the semiconductorlayer at the same time with the same etching conditions, for example.

In the third aspect of the present invention, the semiconductor devicefurther includes: a first interlayer insulating film that insulates thegate electrode and the source electrode from each other; and a secondinterlayer insulating film disposed between the schottky electrode and asurface of the first conductive type region for a diode outside of thediode trench. With this configuration, it is possible to insulate thegate electrode and the source electrode from each other by the firstinterlayer insulating film, and it is possible to insulate the schottkyelectrode and the surface of the first conductive type region for adiode outside of the diode trench from each other.

In the fourth aspect of the present invention, the first interlayerinsulating film and the second interlayer insulating film have the samethickness.

With this configuration, in manufacturing the semiconductor device, itis possible to form the source trench and the diode trench at the sametime after an interlayer insulating film that becomes the firstinterlayer insulating film and the second interlayer insulating film isformed on the entire surface of the semiconductor layer. Also, thesecond conductive type region for a diode can be formed at the bottom ofthe diode trench at the same time as forming the body contact regionnear the bottom of the source trench. At the side walls of the diodetrench, a schottky barrier diode can be formed. In this case, it is notnecessary to remove the interlayer insulating film. In thisconfiguration, the first interlayer insulating film and the secondinterlayer insulating film can be formed in the same step.

In the fifth aspect of the present invention, the schottky electrode hasa first thickness at the side walls of the diode trench, and a secondthickness that is greater than the first thickness on the secondinterlayer insulating film.

If the thickness of a portion of the schottky electrode forming aschottky junction with the first conductive type region for a diodediffers depending on places, a plurality of schottky barrier diodeshaving slightly different forward voltages (Vf) are connected inparallel, which can cause the characteristics of the entire schottkybarrier diodes to be unstable. By contrast, with the configuration ofthe invention according to claim 5, only the portion of the schottkyelectrode having the first thickness forms the schottky junction withthe first conductive type region for a diode at the side walls of thediode trench, and the portion of the schottky electrode having thesecond thickness does not form the schottky junction with the firstconductive type region for a diode. As a result, the portion of theschottky electrode forming the schottky junction with the firstconductive type region for a diode has a uniform thickness, i.e., thefirst thickness, and because the variation in Vf can be eliminated, theoverall characteristics of the schottky barrier diode can be madestable.

In the sixth aspect of the present invention, a plurality of diodetrenches are formed in the diode forming region with a gap therebetween.

In the seventh aspect of the present invention, the gap between theplurality of diode trenches is set such that depletion layers spreadingfrom the respective pn junctions in a reverse bias state are connectedto each other. With this configuration, in the reverse bias state, thedepletion layers spread and are connected to each other at the bottomportions of adjacent diode trenches, which makes it possible to blockthe path of an electric current in the first conductive type region fora diode more reliably, and therefore, the reverse leak current can bereduced to a greater degree.

In the eighth aspect of the present invention, the schottky electrodeincludes a schottky/ohmic electrode layer that forms a schottky contactwith the first conductive type region for a diode at side walls of thediode trench and that forms an ohmic contact with the second conductivetype region for a diode at a bottom of the diode trench. With thisconfiguration, by forming the schottky/ohmic electrode layer at the sidewalls and bottom of the diode trench, the schottky barrier diode and thepn diode can be formed at the same time.

In the ninth aspect of the present invention, the source electrode andthe schottky electrode are made of the same electrode material. Withthis configuration, the source electrode and the schottky electrode canbe formed in the same step by supplying the electrode material into thesource trench and the diode trench.

The tenth aspect of the present invention is the semiconductor deviceaccording to any one of claims 1 to 9, wherein the source trench isformed at a surface of the semiconductor layer in a linear shape along afirst direction, and wherein the diode trench is formed at the surfaceof the semiconductor layer in a linear shape along a second directionthat is orthogonal to the first direction.

With this configuration, by injecting impurity ions into the sourcetrench and the diode trench at an angle relative to the second directionto form the body contact region and the second conductive type regionfor a diode, the body contact region is formed at the side walls and thebottom of the source trench, and the second conductive type region for adiode is formed at the bottom of the diode trench. However, because theimpurity ions are not injected to a pair of side walls of the diodetrench facing each other along the first direction, the secondconductive type region for a diode is not formed thereat. This allowsthe schottky electrode to form a schottky junction at those side wallsof the diode trench.

In the eleventh aspect of the present invention, the diode trench isrectangular in a plan view.

In the twelfth aspect of the present invention, the source trench isformed at a surface of the semiconductor layer in a linear shape, andtwo parallel sides of the diode trench that is rectangular in a planview are orthogonal to a lengthwise direction of the source trench. Withthis configuration, by injecting impurity ions into the source trenchand the diode trench at an angle relative to the direction orthogonal tothe lengthwise direction of the source trench, to form the body contactregion and the second conductive type region for a diode, the bodycontact region is formed at the side walls and the bottom of the sourcetrench, and the second conductive type region for a diode is formed atthe bottom of the diode trench. However, because the impurity ions arenot injected into a pair of side walls of the diode trench facing eachother along the direction orthogonal to the lengthwise direction of thediode trench, the second conductive type region for a diode is notformed at the side walls. This allows the schottky electrode to form aschottky junction at the side walls of the diode trench.

In the thirteen aspect of the present invention, the source region andthe drain region are arranged with a gap therebetween along a thicknessdirection of the semiconductor layer, the source region and the drainregion having the body region disposed therebetween, a gate trench thatreaches the drain region through the source region and the body regionis further provided, and the gate electrode is embedded in the gatetrench. With this configuration, when a voltage is applied to the gateelectrode, a channel is formed near the gate electrode in the bodyregion, which causes an electric current to flow through the transistor.That is, a trench gate type transistor is constructed.

In the fourteen aspect of the present invention, the diode trench isformed shallower than the gate trench.

In the fifteenth aspect of the present invention, the source region andthe drain region are arranged along the surface of the semiconductorlayer with a gap therebetween. That is, the transistor is a planartransistor.

In the sixteen aspect of the present invention, a manufacturing methodof a semiconductor device includes: forming, in a semiconductor layer ofa first conductive type in which the transistor region and a dioderegion are respectively defined, a body region of a second conductivetype in the transistor region, and leaving the diode region as a firstconductive type region for a diode; forming a source region and a drainregion of the first conductive type so as to be separated from eachother across the body region; forming both a source trench in thesemiconductor layer and a diode trench in the diode region at the sametime, the source trench reaching the body region through the sourceregion; injecting an impurity ion into the semiconductor layer near abottom of the source trench and near a bottom of the diode trench toform, at the same time, a body contact region near the bottom of thesource trench and in the semiconductor layer that includes the bodyregion, and a second conductive type region for a diode near the bottomof the diode trench in the semiconductor layer, the body contact regionbeing the second conductive type and having a higher impurityconcentration than that of the body region, the second conductive typeregion for a diode forming a pn junction with the first conductive typeregion for a diode; forming a gate electrode facing through a gateinsulating layer the body region that lies between the source region andthe drain region; and embedding a source electrode in the source trenchat the same time as forming a schottky electrode that forms a schottkyjunction with the first conductive type region for a diode at side wallsof the diode trench.

With this method, in the completed semiconductor device, a transistor isformed in the transistor region, and in the diode region, a pn diode isformed at the bottom of the diode trench, and a schottky barrier diodeis formed at the side walls of the diode trench. In this case, thesource trench and the diode trench can be formed at the same time. Also,it is possible to form the body contact region at the bottom of thesource trench at the same time as forming the second conductive typeregion for a diode at the bottom of the diode trench. Furthermore, it ispossible to embed the source electrode in the source trench at the sametime as forming the schottky electrode in the diode trench. In this way,the transistor and the diode can be formed at the same time, andtherefore, it is possible to eliminate a process that is necessary whenthe transistor and the diode are formed in different processes (such asa process of forming a protective film on the surface of thesemiconductor layer, and removing the protective film from the dioderegion after forming the source trench). As a result, the semiconductordevice can be manufactured at low cost.

Also, in the completed semiconductor device, in the reverse bias state,a depletion layer spreads around the second conductive type region for adiode at the bottom of the diode trench, and because the path of anelectric current in the diode region is thereby blocked, the reverseleak current can be reduced.

In the seventeenth aspect of the present invention, the manufacturingmethod further includes: forming, before forming the source electrodeand the schottky electrode, a first interlayer insulating film forinsulating the gate electrode and the source electrode from each otherat the same time as forming a second interlayer insulating filminterposed between the schottky electrode and the surface of the firstconductive type region for a diode outside of the diode trench.

With this method, in the completed semiconductor device, the gateelectrode and the source electrode can be insulated from each other bythe first interlayer insulating film, and the schottky electrode and thesurface of the first conductive type region for a diode outside of thediode trench can be insulated from each other by the second interlayerinsulating film. Because the first and second interlayer insulatingfilms are formed in the same step, the number of manufacturing steps canbe reduced.

In the eighteenth aspect of the present invention, a plurality of diodetrenches are formed in the diode region with a gap therebetween, and thegap between the plurality of diode trenches is set such that a depletionlayer spreading from each pn junction is connected to one another in thereverse bias state.

With this method, in the completed semiconductor device, in the reversebias state, the depletion layers spread and are connected to each otherat the bottom of adjacent diode trenches, which makes it possible toblock the path of an electric current in the first conductive typeregion for a diode more reliably, and therefore, the reverse leakcurrent can be reduced to a greater degree.

In the nineteenth aspect of the present invention, the source trench isformed at a surface of the semiconductor layer in a linear shape along afirst direction, and the diode trench is formed at the surface of thesemiconductor layer in a linear shape along a second direction that isorthogonal to the first direction.

With this configuration, by injecting impurity ions into the sourcetrench and the diode trench at an angle relative to the seconddirection, to form the body contact region and the second conductivetype region for a diode, the body contact region is formed at the sidewalls and the bottom of the source trench, and the second conductivetype region for a diode is formed at the bottom of the diode trench.However, because the impurity ions are not injected into a pair of sidewalls of the diode trench facing each other along the first direction,the second conductive type region for a diode is not formed at the sidewalls. This allows the schottky electrode to form a schottky junction atthe side walls of the diode trench.

In the twentieth aspect of the present invention, the source trench isformed in a linear shape at the surface of the semiconductor layer, thediode trench is formed to be rectangular in a plan view, and twoparallel sides of the diode trench that is rectangular in a plan vieware orthogonal to a lengthwise direction of the source trench.

With this method, by injecting impurity ions into the source trench andthe diode trench at an angle relative to the direction orthogonal to thelengthwise direction of the source trench, to form the body contactregion and the second conductive type region for a diode, the bodycontact region is formed at the side walls and the bottom of the sourcetrench, and the second conductive type region for a diode is formed atthe bottom of the diode trench. However, because the impurity ions arenot injected to a pair of side walls of the diode trench facing eachother along the direction orthogonal to the lengthwise direction of thediode trench, the second conductive type region for a diode is notformed at the side walls. This allows the schottky electrode to form aschottky junction at the side walls of the diode trench.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a semiconductor device of anembodiment of the present invention.

FIG. 2 is a schematic plan view of a semiconductor device of anotherembodiment of the present invention.

FIG. 3 is an enlarged view of a main part of the semiconductor device ofFIG. 1 or 2.

FIG. 4 is a diagram showing a modification example of a main part of thesemiconductor device of FIG. 3.

FIG. 5 is a perspective view near a cross section along the cut line V-Vof FIG. 3 or 4.

FIG. 6 is a cross-sectional view along the cut line V-V of FIG. 3 or 4.

FIG. 7A is an illustrative cross-sectional view showing a manufacturingmethod of the semiconductor device of FIG. 6.

FIG. 7B is an illustrative cross-sectional view showing a step thatfollows FIG. 7A.

FIG. 7C is an illustrative cross-sectional view showing a step thatfollows FIG. 7B.

FIG. 7D is an illustrative cross-sectional view showing a step thatfollows FIG. 7C.

FIG. 7E is an illustrative cross-sectional view showing a step thatfollows FIG. 7D.

FIG. 7F is an illustrative cross-sectional view showing a step thatfollows FIG. 7E.

FIG. 7G is an illustrative cross-sectional view showing a step thatfollows FIG. 7F.

FIG. 7H is an illustrative cross-sectional view showing a step thatfollows FIG. 7G.

FIG. 7I is an illustrative cross-sectional view showing a step thatfollows FIG. 7H.

FIG. 7J is an illustrative cross-sectional view showing a step thatfollows FIG. 7I.

FIG. 8 is an illustrative cross-sectional view of a semiconductor deviceof another embodiment of the present invention.

FIG. 9 is a perspective view that schematically shows a semiconductorpackage according to an embodiment of the present invention.

FIG. 10 is a circuit diagram of a DC-DC converter that uses thesemiconductor device of the present invention.

FIG. 11 is a diagram showing a modification example of a main part ofthe semiconductor device of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, embodiments of the present invention will be explained in detailwith reference to appended drawings.

FIG. 1 is a schematic plan view of a semiconductor device of anembodiment of the present invention. FIG. 2 is a schematic plan view ofa semiconductor device of another embodiment of the present invention.

A semiconductor device 1 of an embodiment of the present invention isformed to be a quadrangular chip in a plan view. The length of each ofthe four sides of the semiconductor device 1 in a plan view isapproximately several mm, for example.

On the surface of the semiconductor device 1 having a quadrangular shapein a plan view, an external connection region A is formed along oneside, and in a region other than the external connection region A, anactive region B is formed. The semiconductor device 1 includes aplurality of external electrodes 2 disposed in the external connectionregion A, a guard ring 3 surrounding the active region B, a plurality ofdiode forming regions C disposed in the active region B, and atransistor forming region D defined as a region of the active region Bwhere the diode forming regions C are not formed.

The plurality of (seven in this example) external electrodes 2 aredisposed along one side of the quadrangle. Each external electrode 2 isconnected to a lead (not shown) through a bonding wire (not shown) asdescribed below. The guard ring 3 separates and insulates the externalconnection region A and the active region B from each other.

The plurality of diode forming regions C are dispersed so as to bedistributed uniformly in the entire active region B. Specifically, theplurality of diode forming regions C may be arranged in a staggeredpattern with a gap therebetween as shown in FIG. 1, or may be arrangedin a matrix as shown in FIG. 2.

FIG. 3 is an enlarged view of a main part of the semiconductor device ofFIG. 1 or 2. FIG. 4 is a diagram showing a modification example of themain part of the semiconductor device of FIG. 3.

FIG. 3 shows a portion surrounded by a dotted line in FIG. 1 or 2 (onediode forming region C and the transistor forming region D therearound).

Each diode forming region C is in a square shape in a plan view. In aplan view, each diode forming region C is surrounded by the transistorforming region D.

In the diode forming region C, schottky barrier diodes 10 and pn diodes45 are formed, and in the transistor forming region D, a plurality oftransistor cells 11A are formed. The plurality of transistor cells 11Aare connected in parallel, and form one transistor 11 altogether (seeFIG. 1). The transistor 11 includes a plurality of schottky barrierdiodes 10 and pn diodes 45 (see FIG. 1). As described above, in theactive region B of the semiconductor device 1, the transistor 11 isformed surrounding the plurality of schottky barrier diodes 10 and pndiodes 45 (see FIG. 1). Accordingly, in the semiconductor device 1, thetransistor 11, the schottky barrier diodes 10, and the pn diodes 45 areformed in the same element.

For the plurality of transistor cells 11A (transistor 11), gate trenches12 and source trenches 13, which will be described later, are formedthroughout substantially the entire surface of the semiconductor device1 (to be more specific, a front surface 22A of a semiconductor layer 22to be described later) in the transistor forming region D. The gatetrenches 12 and the source trenches 13 are extended in a linear shapealong the first direction Y in a plan view, and are alternately arrangedside by side along the second direction X that is orthogonal to thefirst direction Y with a gap therebetween. That is, the gate trenches 12and the source trenches 13 are formed in a stripe pattern.

Of the gate trench 12 and the source trench 13, the source trench 13 isformed nearest to the diode forming region C. The source trench 13 thatis nearest to the diode forming region C is in a square ring shape thatsurrounds the entire diode forming region C. The gate trench 12 adjacentto the source trench 13 that is nearest to the diode forming region C isin a square ring shape that surrounds the entire source trench 13.

As shown in FIG. 4, the gate trenches 12 and the source trenches 13 maybe arranged such that the gate trench 12 has a mesh-like pattern,thereby partitioning each of a plurality of rectangular regions, and ineach of the rectangular regions, a source trench 13 is extended linearlyso as not to touch the gate trench 12. In this case also, the sourcetrench 13 that is nearest to the diode forming region C is in a squarering shape that surrounds the entire diode forming region C, and thegate trench 12 adjacent to this source trench 13 is in a square ringshape that surrounds the entire source trench 13.

For the schottky barrier diodes 10 and the pn diodes 45, diode trenches14, which will be described later, are formed at the surface of thesemiconductor device 1 in substantially the entire diode forming regionC (to be more specific, the front surface 22A of the semiconductor layer22, which will be described later). The diode trenches 14 extendlinearly along the second direction X in a plan view, and are arrangedside by side along the first direction Y with a gap therebetween. Thatis, in a plan view, each diode trench 14 is formed in a narrowrectangular shape longer in the second direction X, and a plurality ofdiode trenches 14 are formed in a stripe pattern. In each diode trench14 that is rectangular in a plan view, two parallel sides (two sidesextending in the second direction X) H are orthogonal to the lengthwisedirection (first direction Y) of the source trench 13.

FIG. 5 is a perspective view near a cross section along the cut line V-Vof FIG. 3 or 4.

For ease of explanation, FIG. 5 shows the source trenches 13 and thediode trenches 14, but omits the gate trenches 12. As shown in FIG. 5,the source trenches 13 formed in a linear shape along the firstdirection Y and the diode trenches 14 formed in a linear shape along thesecond direction X extend orthogonally to each other.

FIG. 6 is a cross-sectional view along the cut line V-V of FIG. 3 or 4.Because the cut line V-V is bent at a right angle halfway (see FIGS. 3and 4), two cross sections (cross section in the diode forming region Cand cross section in the transistor forming region D) orthogonallyintersect with each other in the actual device, but for ease ofexplanation, FIG. 6 shows the two cross sections along the same plane(the same is true for FIGS. 7A to 7J, and FIG. 8 below).

As shown in FIG. 6, the semiconductor device 1 includes a semiconductorsubstrate 20, a rear electrode 21, a semiconductor layer 22, a gateinsulating film 23, gate electrodes 24, an oxide film 25, an insulatinglayer 26, a first metal film 27, a second metal film 29, sourceelectrodes 28, and a conductive layer 30.

The semiconductor substrate 20 is made of an n⁺ semiconductor (silicon,for example) with a prescribed concentration (1×10¹⁹ to 5×10¹⁹ atom/cm³,for example).

The rear electrode 21 covers the entire rear surface (lower surface inFIG. 6) of the semiconductor substrate 20. The rear electrode 21 is madeof a metal (such as gold, nickel silicide, and cobalt silicide, forexample) that forms an ohmic contact with n-type silicon. Therefore, therear electrode 21 forms an ohmic contact with the rear surface of thesemiconductor substrate 20.

The semiconductor layer 22 is formed on the front surface (upper surfacein FIG. 6) of the semiconductor substrate 20. The semiconductor layer 22is made of an n⁻ semiconductor having a lower concentration than thesemiconductor substrate 20 (5×10¹⁵ to 5×10¹⁶ atom/cm³, for example). Inthe semiconductor layer 22 of FIG. 6, the upper surface is referred toas a front surface 22A and the lower surface is referred to as a rearsurface 22B. The thickness of the entire semiconductor layer 22 is 4 μm,for example. The semiconductor layer 22 and the semiconductor substrate20 may be collectively regarded as a semiconductor layer.

In the semiconductor layer 22, the diode forming region C and thetransistor forming region D are defined as described above. Thesemiconductor layer 22 in the transistor forming region D is referred toas a transistor region 35, and the semiconductor layer 22 in the diodeforming region C is referred to as an n-type region 40 for a diode. FIG.6 shows a part of the semiconductor layer 22 near the boundary betweenthe diode forming region C and the transistor forming region D. Thefront surface 22A and the rear surface 22B of the semiconductor layer 22are flat throughout the entire diode forming region C and the transistorforming region D, and extend parallel to each other.

In the entire surface portion of the semiconductor layer 22 in thetransistor forming region D (transistor region 35), a p⁻ body region 31having a prescribed impurity concentration (1×10¹⁶ to 1×10¹⁷ atom/cm³,for example) is formed. A region of the transistor region 35 closer tothe rear surface 22B than the body region 31 is an n⁻ drain region 34.On the other hand, the semiconductor layer 22 in the diode formingregion C is the abovementioned n-type region 40 for a diode, which is ofan n⁻ type. Near the surface of the body region 31, an n⁺ source regions32 having a prescribed impurity concentration (5×10¹⁹ to 5×10²⁰atom/cm³, for example) is selectively formed. Therefore, the body region31 lies between the source region 32 and the drain region 34 along thethickness direction of the semiconductor layer 22. In other words, inthe transistor region 35, the source region 32 and the drain region 34are formed so as to be separated from each other across the body region31 (along the thickness direction of the semiconductor layer 22). Thesurface of the source region 32 and the surface of the body region 31 ina region where the source region 32 is not formed are flush with eachother, constituting the front surface 22A of the semiconductor layer 22(transistor region 35) in the transistor forming region D. The thicknessof the source region 32 is approximately 0.2 μm, for example, and thethickness of a portion of the body region 31 closer to the rear surface22B than the source region 32 is approximately 0.4 μm, for example.

In the semiconductor layer 22 in the transistor forming region D, theabove-mentioned gate trenches 12 are formed. Each gate trench 12 isrecessed from the front surface 22A toward the rear surface 22B of thesemiconductor layer 22 in the transistor forming region D. The gatetrench 12 penetrates both the source region 32 and the body region 31,reaching the inside of the drain region 34. The bottom surface of thegate trench 12 is given the reference character 12A. The trench width ofthe gate trench 12 is approximately 0.2 μm, and the depth thereof isapproximately 1 μm, for example.

The gate insulating film 23 is made of silicon oxide (SiO₂), and isformed so as to make contact with the entire inner surface (side wallsurfaces and bottom wall surface) of each gate trench 12. The gateinsulating film 23 makes contact with the body region 31 at the sidewall surfaces of the gate trench 12, and makes contact with the drainregion 34 at the bottom wall surface of the gate trench 12.

The gate electrode 24 is made of polysilicon, for example. The gateelectrode 24 is embedded in the gate insulating film 23 in each gatetrench 12. The gate electrode 24 faces surfaces (portions exposed in thegate trench 12) of the body region 31 (between the source region 32 andthe drain region 34) and the drain region 34 through the gate insulatingfilm 23.

The oxide film 25 is made of SiO₂, and covers substantially the entirefront surface 22A of the semiconductor layer 22 in the transistorforming region D and the diode forming region C.

The insulating layer 26 is made of glass such as BPSG (boron phosphorsilicate glass), and is formed on the oxide film 25. The layered oxidefilm 25 and insulating layer 26 constitute an interlayer insulating film48. The thickness of the interlayer insulating film 48 is approximately0.5 μm, for example. The interlayer insulating film 48 includes a firstinterlayer insulating film 48A formed in the transistor forming regionD, and a second interlayer insulating film 48B formed in the diodeforming region C. The first interlayer insulating film 48A and thesecond interlayer insulating film 48B have the same thickness.

The above-mentioned source trench 13 is recessed from the surface of theinsulating layer 26 (upper surface in FIG. 6), and reaches the inside ofthe body region 31, penetrating the insulating layer 26, the oxide film25 (first interlayer insulating film 48A), and the source region 32 inthe semiconductor layer 22. The source trenches 13 are formed inpositions other than where the gate trenches 12 are formed in thesemiconductor layer 22 in the transistor forming region D, and arerecessed from the front surface 22A of the semiconductor layer 22 inthese positions. The trench width of the source trench 13 isapproximately 0.2 μm, and the depth thereof is approximately 0.3 μm, forexample. The distance P between the bottom surface 13A of the sourcetrench 13 and the rear surface 22B of the semiconductor layer 22 isgreater than the distance Q between the bottom surface 12A of the gatetrench 12 and the rear surface 22B of the semiconductor layer 22. Thatis, the source trench 13 is formed shallower than the gate trench 12. Ina plan view, an end of the body region 31 closer to the diode formingregion C coincides with the center of the bottom surface 13A in thewidth direction of the source trench 13 that is closest to the diodeforming region C (the rightmost source trench 13 in FIG. 6).

At the bottom surface 13A of the source trench 13 in the body region 31and the periphery thereof (bottom portion of the source trench 13), a p⁺body contact region 33 is formed. The body contact region 33 has ahigher impurity concentration (5×10¹⁸ to 5×10¹⁹ atom/cm³, for example)than that of the p⁻ body region 31.

The above-mentioned diode trenches 14 are recessed from the frontsurface of the insulating layer 26 (upper surface in FIG. 6), andreaches the inside of the n-type region 40 for a diode in thesemiconductor layer 22, penetrating the insulating layer 26 and theoxide film 25 (second interlayer insulating film 48B). As describedabove, the diode trench 14 is formed extending along the seconddirection X, and a plurality of diode trenches 14 are formed along thefirst direction Y with a gap therebetween in the n-type region 40 for adiode (see FIGS. 3 and 4). The distance R between the bottom surface 14Aof each diode trench 14 and the rear surface 22B of the semiconductorlayer 22 is the same as the distance P between the bottom surface 13A ofthe source trench 13 and the rear surface 22B of the semiconductor layer22, and is greater than the distance Q between the bottom surface 12A ofthe gate trench 12 and the rear surface 22B of the semiconductor layer22. That is, the source trench 13 and the diode trench 14 have the samedepth, and are formed shallower than the gate trench 12.

At the bottom of the diode trench 14 (portion immediately below thebottom surface 14A) in the n-type region 40 for a diode, a p⁺ region 41for a diode, which is of a p⁺ type and has substantially the sameimpurity concentration as that of the body contact region 33, is formed.The p⁺ region 41 for a diode forms a pn junction with the n-type region40 for a diode, which is of an n⁺ type.

The first metal film 27 is made of a metal that forms a schottkyjunction by joining with n⁻-type silicon. Examples of such a metalinclude titanium (Ti), molybdenum (Mo), palladium (Pd), titanium nitride(TiN), titanium silicide, molybdenum silicide, tungsten silicide, andcobalt silicide. These metals form a schottky junction with an n⁻semiconductor, and forms an ohmic junction with n⁺ and p⁺semiconductors. The first metal film 27 is formed to make contact withthe entire front surface of the first interlayer insulating film 48A(upper surface in FIG. 6) and the entire inner surfaces of each sourcetrench 13, and in this state, the first metal film 27 is electricallyconnected to the source region 32 and the body contact region 33(forming an ohmic contact). As described above, the source trenches 13are formed to make contact with the source region 32 and the bodycontact region 33.

The first metal film 27 is also formed so as to make contact with theentire front surface of the second interlayer insulating film 48B (uppersurface in FIG. 6) and the entire inner surfaces of each diode trench14, and in this state, the first metal film 27 forms an ohmic contactwith the p⁺ region 41 for a diode, and forms a schottky junction withthe n-type region 40 for a diode at side walls 14B of the diode trench14.

The source electrodes 28 are made of tungsten, for example. The sourceelectrode 28 is embedded in each source trench 13 so as to fill theinner space of the source trench 13 where the first metal film 27 isformed. The first metal film 27 in the source trench 13 functions as apart of the source electrode 28. The first interlayer insulating film48A is formed covering the gate electrodes 24, and the source electrodes28 are formed in the first interlayer insulating film 48A in positionswhere the gate electrodes 24 are not formed. This way, because the firstinterlayer insulating film 48A is interposed between a gate electrode 24and a source electrode 28 adjacent to each other, the adjacent gateelectrode 24 and source electrode 28 can be insulated from each other bythe first interlayer insulating film 48A.

The second metal film 29 is made of titanium or titanium nitride, andcovers the entire surface of the first metal film 27 and the surface ofeach source electrode 28 that is exposed from the source trench 13(upper surface in FIG. 6). In the diode forming region C, the layeredfirst metal film 27 and second metal film 29 constitute a schottkyelectrode 42. The schottky electrode 42 includes the first metal film 27as a schottky/ohmic electrode layer that forms a schottky contact withthe n-type region 40 for a diode at the side walls 14B of the diodetrench 14 and that forms an ohmic contact with the p⁺ region 41 for adiode at the bottom (around the bottom surface 14A) of the diode trench14. The thickness of the schottky electrode 42 is 200 Å to 300 Å.

The front surface 22A of the semiconductor layer 22 in a portion of thediode region where the diode trenches 14 are not formed is entirelycovered by the second interlayer insulating film 48B, and the frontsurface (upper surface in FIG. 6) and the side faces (constituting sidewalls 14B of the diode trench 14) of the second interlayer insulatingfilm 48B are covered by the schottky electrode 42. That is, the secondinterlayer insulating film 48B is disposed (interposed) between theschottky electrode 42 and the surface (front surface 22A of thesemiconductor layer 22) of the diode region outside of the diodetrenches 14. By the second interlayer insulating film 48B, the schottkyelectrode 42 and the surface of the diode region outside of the diodetrenches 14 are insulated from each other.

The conductive layer 30 is made of an alloy of aluminum and copper (AlCualloy), for example. The conductive layer 30 is layered on the secondmetal film 29, and covers the entire surface (upper surface in FIG. 6)of the second metal film 29. The conductive layer 30 is electricallyconnected to corresponding electrodes out of the plurality of externalelectrodes 2 mentioned above (see FIGS. 1 and 2). The gate electrodes 24are electrically connected to other corresponding external electrodes 2via not-shown relay wiring lines.

In the transistor forming region D, the conductive layer 30, the secondmetal film 29, the source electrodes 28, the first metal film 27, thesource region 32, and the body contact region 33 are electricallyconnected. The rear electrode 21, the semiconductor substrate 20, andthe drain region 34 that is formed in a region of the semiconductorlayer 22 closer to the semiconductor substrate 20 than the body region31 are electrically connected.

This way, in the transistor forming region D, transistor cells 11A areconstructed individually. The transistor cell 11A (transistor 11) hasgate trenches 12 in which the gate electrodes 24 are embedded, and istherefore a so-called trench gate MOSFET (metal oxide semiconductorfield effect transistor). In the transistor cell 11A, a parasitic diodeis formed by the body region 31 and the drain region 34.

For example, in a state where the source electrodes 28 (conductive layer30) are grounded and a positive voltage is applied to the rear electrode21, a voltage equal to or greater than a threshold voltage is applied tothe gate electrodes 24. As a result, a channel is formed in a channelregion X near the boundary between the body region 31 and the gateinsulating film 23 outside of the gate electrodes 24, allowing anelectric current to flow toward the source electrode 28 from the rearelectrode 21 via the channel.

In the diode forming region C, the rear electrode 21 forms an ohmiccontact with the semiconductor substrate 20, and the first metal film 27(schottky electrode 42) forms a schottky junction with the n-type region40 for a diode at the side walls 14B of the diode trench 14, therebyconstituting a schottky barrier diode 10. The schottky barrier diode 10and the transistor 11 are connected to each other in parallel. Also, thep+ region 41 for a diode at the bottom surface 14A of each diode trench14 forms a pn junction with the n-type region 40 for a diode in thediode forming region C, and with the pn junction between the p+ region41 for a diode and the n-type region 40 for a diode, a pn diode 45 isconstituted. As described above, in one diode trench 14, the pn diode 45is formed at the bottom surface 14A, and the schottky barrier diode 10is formed at the side walls 14B.

In each diode trench 14 in the diode forming region C, the schottkybarrier diode 10 and the pn diode 45 are connected to each other inparallel. The forward voltage (Vf) of the schottky barrier diode 10 islower than Vf of the pn diode 45 (0.6V to 0.7V, for example), andtherefore, an electric current flows through the schottky barrier diode10 before the pn diode 45.

In a reverse bias state, a depletion layer 80 spreads from the pn diode45 at the bottom of each diode trench 14, and respective depletionlayers 80 at the bottom of adjacent diode trenches 14 are connected toeach other. In other words, the gap between the plurality of diodetrenches 14 is set such that the depletion layers 80 each spreading fromthe pn junction between the p+ region 41 for a diode and the n-typeregion for a diode are connected to each other in the reverse biasstate. By the depletion layers 80 spreading and connecting to each othernear the pn diodes 45 at the bottom of the diode trenches 14, the pathof an electric current in the diode forming region is blocked, therebymaking it possible to reduce the reverse leak current.

The second interlayer insulating film 48B does not have to be formed,and it is also possible to omit the second insulating film 48B so as toincrease the area of the schottky junction between the schottkyelectrode 42 and the n-type region for a diode. However, the thicknessof the schottky electrode 42 on the surface (front surface 22A) of then-type region for a diode, and the thickness of the schottky electrode42 at the side walls 14B of the diode trench 14 do not necessarilybecome equal to each other, possibly causing the characteristics to beunstable. In other words, if the thickness of a portion of the schottkyelectrode 42 that forms a schottky junction with the n-type region for adiode differs depending on places, a plurality of schottky barrierdiodes 10 having slightly different forward voltages (Vf) are connectedin parallel, which can cause the characteristics of the entire schottkybarrier diodes 10 to be unstable.

In order to address this problem, in the semiconductor device 1 of thepresent embodiment, the second interlayer insulating film 48B is left,instead of being removed. In this case, the schottky electrode 42 has afirst thickness T at the side walls 14B of the diode trench 14, and hasa second thickness U that is greater than the first thickness T on thesecond interlayer insulating film 48B.

In the semiconductor device 1, only the portion of the schottkyelectrode 42 having the first thickness T forms a schottky junction withthe n-type region for a diode at the side walls 14B of the diode trench14, and the portion of the schottky electrode 42 with the secondthickness U does not form a schottky junction with the n-type region fora diode. As a result, the portion of the schottky electrode 42 thatforms the schottky junction with the n-type region for a diode has auniform thickness, i.e., the first thickness T, and because thevariation in Vf can be eliminated, the overall characteristics of theschottky barrier diode 10 can be made stable. This makes it possible toimprove the overall performance of the semiconductor device 1. Also,because it is possible to omit the step of removing the secondinterlayer insulating film 48B in manufacturing the semiconductor device1, the number of manufacturing steps can be reduced, thereby reducingthe cost.

FIGS. 7A to 7J are illustrative cross-sectional views showing amanufacturing method of the semiconductor device of FIG. 6.

First, as shown in FIG. 7A, the semiconductor substrate 20 is made by aknown method.

Next, as shown in FIG. 7B, on the semiconductor substrate 20, thesemiconductor layer 22 of an n⁻-type is formed through the epitaxialgrowth on the surface of the semiconductor substrate 20. In thesemiconductor layer 22, a transistor region 35 corresponding to thetransistor forming region D, and an n-type region 40 for a diodecorresponding to the diode forming region C are defined.

Next, as shown in FIG. 7C, a resist pattern 46 covering the diodeforming region C and exposing only the transistor forming region D(transistor region 35) is formed on the semiconductor layer 22. Next, ap-type impurity (boron, for example) is injected into a surface portionof the semiconductor layer 22 in the transistor forming region D(transistor region 35). Thereafter, the resist pattern 46 is removed,and by conducting annealing, the p-type impurity is activated. As aresult, as shown in FIG. 7C, the p⁻ body region 31 is formed in thesurface portion of the transistor region 35. On the other hand, the n⁻type diode forming region remains intact. In the semiconductor layer 22in the transistor forming region D, a portion closer to thesemiconductor substrate 20 than the body region 31 is the drain region34.

Next, in the surface portion of the body region 31, n-type impurity ions(arsenic or phosphorus, for example) are selectively injected.Thereafter, by conducting annealing, the n-type impurity is activated,and as shown in FIG. 7D, the source region 32 is formed in the surfaceportion of the body region 31.

Next, through etching that uses a resist pattern (not shown) as a mask,recesses are formed in the semiconductor layer 22 from the front surface22A. As a result, as shown in FIG. 7E, gate trenches 12 are formed inthe semiconductor layer 22 in the transistor forming region D.

Next, by the CVD (chemical vapor deposition) method, as shown in FIG.7F, the gate insulating film 23 made of SiO₂ is formed to cover theentire inner surfaces of the gate trenches 12.

Next, as shown in FIG. 7G, a gate electrode 24 made of polysilicon isembedded inside of the gate insulating film 23 in each gate trench 12.

Next, by the CVD method, for example, a film made of SiO₂ (SiO₂ film) 36is formed on the entire front surface 22A of the semiconductor layer 22in both the diode forming region C and the transistor forming region D.The SiO₂ film 36 becomes the oxide film 25.

Next, by conducting CVD in high density, a layer made of glass such asBPSG (glass layer) 37 is formed on the SiO₂ film 36. FIG. 7G shows astate immediately after the glass layer 37 is formed. The glass layer 37becomes the insulating layer 26. By forming the glass layer 37 on theSiO₂ film 36 in this manner, the above-mentioned interlayer insulatingfilm 48 is formed.

Next, by conducting etching that uses a resist pattern (not shown) as amask, the glass layer 37, the SiO₂ layer 36, and the semiconductor layer22 are etched in this order in the diode forming region C and thetransistor forming region D, thereby forming recesses. In this way, asshown in FIG. 7H, a plurality of diode trenches 14 are formed in thediode forming region C, and at the same time, a plurality of sourcetrenches 13 are formed in the transistor forming region D. The bottomsurface 14A of each diode trench 14 and the bottom surface 13A of eachsource trench 13 are located at the same position in terms of the depthdirection of the semiconductor layer 22, and are at the same level.Because the diode trenches 14 and the source trenches 13 are formed inthe same process (that is, with the same conditions), the diode trenches14 and the source trenches 13 have the same depth.

Next, as shown in FIG. 7I, p-type impurity ions (boron, for example) areselectively injected into the surface portions of the semiconductorlayer 22 through the bottom of each source trench 13 (bottom surface 13Aand the periphery thereof) and the bottom of each diode trench 14(bottom surface 14A and the periphery thereof). As indicated with thebroken lines in FIG. 5, the impurity ions are injected toward therespective bottom portions of the source trenches 13 and the diodetrenches 14 at a prescribed angle (approximately ±7°, for example)relative to the thickness direction of the semiconductor substrate 20(in a direction inclined along the second direction X) in the planealong the second direction X (direction orthogonal to the lengthwisedirection of the source trench 13).

Therefore, as in FIG. 7I, when respective cross sections of the sourcetrenches 13 and the diode trenches 14 along the respective widthwisedirections are shown on the same plane, the impurity ions are injectedto the source trenches 13 along the direction that is inclined relativeto the depth direction, and the impurity ions are injected to the diodetrenches 14 along the depth direction as indicated with the brokenarrows. As a result, in each source trench 13 in the semiconductor layer22, the impurity ions are injected into the bottom surface 13A and apair of side walls 13B facing along the widthwise direction (theabove-mentioned second direction X). In each diode trench 14 in thesemiconductor layer 22, while the impurity ions are injected into thebottom surface 14A and a pair of side walls 14C (see FIG. 5) facingalong the lengthwise direction (the above-mentioned second direction X),almost no impurity ions are injected into a pair of side walls 14Bfacing along the widthwise direction (the above-mentioned firstdirection Y).

Thereafter, by conducting annealing, the p-type impurity (ions injectedin the previous step) is activated, forming the body contact region 33in the body region 31 at the side walls 13B and the bottom of eachsource trench 13 and, at the same time, forming the p⁺ region 41 for adiode at the bottom of each diode trench 14 in the n-type region 40 fora diode. The p⁺ region 41 for a diode is formed in a portion immediatelybelow the bottom surface 14A of the diode trench 14 and at the sidewalls 14C of the diode trench 14 (see FIG. 5). However, at the pair ofside walls 14B (facing along the above-mentioned first direction Y) ofthe diode trench 14, the impurity ion injection was suppressed asdescribed above, and therefore, the p⁺ region 41 for the diode is notformed. This allows the schottky electrode 42 to form a schottkyjunction at the side walls 14B of the diode trench 14 as describedbelow.

Next, as shown in FIG. 7J, by sputtering or the like, the first metalfilm 27 made of titanium is formed on the entire inner surfaces of thesource trenches 13 and the diode trenches 14 (portions of the oxide film25, the insulating layer 26, and the semiconductor layer 22 that areexposed in each trench) and the entire surface of the insulating layer26 (interlayer insulating film 48).

Next, a source electrode 28 made of tungsten is embedded inside of thefirst metal film 27 in each source trench 13. FIG. 7J shows a stateimmediately after the source electrodes 28 are embedded.

Next, by sputtering or the like, the second metal film 29 made oftitanium is formed on the entire surface of the first metal film 27 andthe surface of each source electrode 28 that is exposed from the sourcetrench 13, and thereafter, the conductive layer 30 made of aluminum isformed on the second metal film 29. Next, by forming the rear electrode21 on the rear surface of the semiconductor substrate 20, as shown inFIG. 6, each transistor cell 11A (transistor 11), schottky barrier diode10, and pn diode 45 are completed at the same time, thereby completingthe semiconductor device 1.

The source electrodes 28 (including the first metal film 27 in thesource trenches 13) and the schottky electrode 42 (constituted of thefirst metal film 27 and the second metal film 29) may be made of thesame electrode material (specifically the material of the first metalfilm 27). In this case, the schottky electrode 42 is formed at the sametime as embedding the source electrode 28 in each source trench 13. Thatis, by supplying the electrode material into each source trench 13 andeach diode trench 14, the source electrodes 28 and the schottkyelectrode 42 can be formed in the same process. Also, by forming theschottky electrode 42 (especially the first metal film 27) at the sidewalls 14B and the bottom (bottom surface 14A) of each diode trench 14,the schottky barrier diode 10 and the pn diode 45 can be formed at thesame time.

The schottky electrode 42 (first metal film 27 and second metal film 29)is formed by sputtering or the like in which it is harder for a metalmaterial (titanium as described above) to be deposited on the side walls14B of each diode trench 14, and therefore, the thickness thereofbecomes greater on the bottom surfaces 14A and on the second interlayerinsulating film 48B than on the side walls 14B.

As described above, in the semiconductor device 1, the transistor 11 isformed in the transistor region 35, which is a region of thesemiconductor layer 22 outside of the diode forming region, and in thediode forming region, the pn diode 45 is formed at the bottom of eachdiode trench 14, and the schottky barrier diode 10 is formed at the sidewalls 14B of each diode trench 14. In this case, the source trenches 13and the diode trenches 14 can be formed at the same time (see FIG. 7H).Also, it is possible to form the body contact region 33 at the bottom ofeach source trench 13 at the same time as forming the p⁺ region 41 for adiode at the bottom of each diode trench 14 (see FIG. 7I). Furthermore,it is possible to embed the source electrode 28 in each source trench 13at the same time as forming the schottky electrode 42 in each diodetrench 14 (see FIG. 7J). As a result, the transistor 11 and the diodes(schottky barrier diodes 10 and pn diodes 45) can be formed at the sametime. Thus, it is possible to omit the process that would be necessarywhen the transistor 11 and the diodes were formed in different processes(such as a process of forming a protective film on the surface of thesemiconductor layer 22, and thereafter removing the protective film fromthe diode region after the source trenches 13 are formed). As describedabove, the diode trenches 14 and the p⁺ region 41 for a diode can beformed by using the process for forming the transistor 11 (that is, aspecial process for forming the diodes is no longer needed), andtherefore, it is possible to fabricate the semiconductor device 1 thathas the transistor 11 and the schottky barrier diodes 10 on the samechip with a smaller number of manufacturing steps. As a result, thesemiconductor device 1 can be manufactured at low cost.

As described above, when manufacturing the semiconductor device 1, theinterlayer insulating film 48 that becomes the first interlayerinsulating film 48A and the second interlayer insulating film 48B isformed on the entire front surface 22A of the semiconductor layer 22(see FIG. 7G), and next, the source trenches 13 and the diode trenches14 are formed at the same time (see FIG. 7H). It is possible to form thep⁺ region 41 for a diode at the bottom of each diode trench 14 at thesame time as forming the body contact region 33 at the bottom of eachsource trench 13 (see FIG. 7I). At the side walls 14B of the diodetrench 14, the schottky barrier diode 10 can be formed (see FIG. 6). Inthis case, it is not necessary to remove the interlayer insulating film48. When forming the source trenches 13 and the diode trenches 14, thefirst interlayer insulating film 48A and the second interlayerinsulating film 48B can be formed in the same step (see FIG. 7H), andtherefore, it is possible to reduce the number of manufacturing steps.Because the first interlayer insulating film 48A and the secondinterlayer insulating film 48B are both left instead of being removed,it is possible to omit the step of removing these interlayer insulatingfilms 48.

In a plan view, the transistor forming region D surrounds the diodeforming regions C (see FIGS. 1 to 4). When the transistor 11 in thetransistor forming region D is ON, the schottky barrier diode 10 in thediode forming region C is turned OFF, thereby making it possible torelease heat from the semiconductor layer 22 through the diode formingregion C. When the transistor 11 is OFF, it is possible to release heatfrom the semiconductor layer 22 through the transistor forming region D.This way, it is possible to prevent the temperature of the semiconductordevice 1 from increasing. In particular, by forming the transistorforming region D so as to surround the diode forming regions C, heatfrom one region can be released through the other region, and therefore,it is possible to effectively mitigate an increase in temperature of thesemiconductor device 1. Also, because a plurality of diode formingregions C are dispersed so as to be distributed evenly with a prescribedgap therebetween, it is possible to more effectively mitigate anincrease in temperature of the semiconductor device 1.

FIG. 8 is an illustrative cross-sectional view of a semiconductor deviceof another embodiment of the present invention.

Next, an embodiment differing from the embodiment above will beexplained. In the embodiment below, parts corresponding to the partsdescribed in the embodiment above are given the same referencecharacters, and detailed descriptions thereof are omitted. In the caseof FIG. 8, the transistor forming region D also surrounds the diodeforming regions C in a plan view (see FIGS. 1 and 2).

A transistor 11 (transistor cells 11A) of a semiconductor device 1 shownin FIG. 8 is a planar type MOSFET that has a different structure fromthat of the embodiment above, and does not have the gate trench 12described above (see FIG. 6). However, the semiconductor device 1 hasthe source trenches 13 and the diode trenches 14.

The semiconductor device 1 shown in FIG. 8 includes the semiconductorsubstrate 20, the rear electrode 21, the semiconductor layer 22, thesource electrodes 28, and the conductive layer 30, which were describedabove, and further includes a gate insulating film 50, gate electrodes51, an insulating film 52, and a metal film 53.

The semiconductor substrate 20 is made of an n⁺ semiconductor. The rearelectrode 21 covers the entire rear surface (lower surface in FIG. 8) ofthe semiconductor substrate 20, and forms an ohmic contact with the rearsurface of the semiconductor substrate 20.

The semiconductor layer 22 is deposited on the front surface (uppersurface in FIG. 8) of the semiconductor substrate 20 by the epitaxialgrowth. The semiconductor layer 22 is made of an n⁻ semiconductor thathas a lower concentration than the semiconductor substrate 20. In thesemiconductor layer 22 of FIG. 8, the upper surface will be referred toas a front surface 22A and the lower surface will be referred to as arear surface 22B. FIG. 8 shows a part of the semiconductor layer 22 nearthe boundary between the diode forming region C and the transistorforming region D. In the semiconductor layer 22, a diode forming regioncorresponding to the diode forming region C, and a transistor region 35corresponding to the transistor forming region D are defined.

In a surface portion of the semiconductor layer 22 in the transistorforming region D, p⁻ body regions 54 are selectively formed. Theplurality of body regions 54 are dispersed throughout the surfaceportion of the semiconductor layer 22. In a surface portion of each bodyregion 54, an n⁺ source region 55 is formed. A region of thesemiconductor layer 22 in the transistor forming region D, except forthe body regions 54, is an n⁻ drain region 56. On the other hand, thesemiconductor layer 22 in the diode forming region C is theabovementioned n-type region 40 for a diode, which is of an n⁻-type.

The surfaces of the source regions 55, the surfaces of the body regions54 where the source regions 55 are not formed, and the surface of thedrain region 56 are flush with each other, forming the front surface 22Aof the semiconductor layer 22 in the transistor forming region D. At thefront surface 22A of the semiconductor layer 22, source regions 55 andthe drain region 56 are located on both sides of the respective bodyregions 54, and are separated from each other with a gap (correspondingto the body region 54 between the source region 55 and the drain region56) therebetween along the front surface 22A.

The gate insulating film 50 is made of SiO₂, and covers portions of thefront surface 22A of the semiconductor layer 22 in the diode formingregion C and the transistor forming region D. The gate insulating film50 in the transistor forming region D is formed covering respectivesource regions 55 adjacent to each other with a gap therebetween at thefront surface 22A of the semiconductor layer 22 in the transistorforming region D.

The gate electrodes 51 are made of polysilicon, for example, and areformed on the gate insulating film 50. Each gate electrode 51 facesthrough the gate insulating film 50 the surface of each body region 54between the source region 55 and the drain region 56.

The insulating film 52 is made of SiO₂. The insulating film 52 coversthe entire surface of each gate electrode 51 except for a portionthereof in contact with the gate insulating film 50. The insulating film52 is connected to the gate insulating film 50.

The source trenches 13 are recessed from the front surface (uppersurface in FIG. 8) of the insulating film 52, and reach the inside ofthe drain region 56, penetrating the insulating film 52 (betweenadjacent gate electrodes 51), the gate insulating film 50, and thesource region 55 and the body region 54 in the semiconductor layer 22.In the body region 54 and around the bottom of each source trench 13 inthe drain region 56, a p⁺ body contact region 58 having a higherimpurity concentration than the body region 54 is formed. The sourceelectrode 28 is embedded in each source trench 13.

The diode trenches 14 are recessed from the front surface of theinsulating film 52, and reach the inside of the n-type region for adiode in the semiconductor layer 22. Near the bottom surface 14A of eachdiode trench 14 in the n-type region for a diode (immediately below thebottom surface 14A), a p+ region 59 for a diode is formed. The p+ region59 for a diode forms a pn junction with the n-type region for a diode,which is of the n⁻-type.

As in the embodiment above, the source trenches 13 and the diodetrenches 14 have the same depth (see FIG. 6).

The metal film 53 includes a metal that forms a schottky junction bycontacting n⁻ silicon (such as titanium, molybdenum, palladium, ortitanium nitride as described above). In the transistor forming regionD, the metal film 53 covers the insulating film 52 and surfaces of thesource electrodes 28 that are exposed from the source trenches 13 (uppersurfaces in FIG. 8). In the diode forming region C, the metal film 53covers the entire front surface (upper surface in FIG. 8) of theinsulating film 52, and is in contact with the entire inner surfaces ofthe diode trenches 14 (including the insulating film 52 and the gateinsulating film 50 that are a part of the inner surfaces). In thisstate, the metal film 53 forms an ohmic contact with the p⁺ region 59for a diode, and forms a schottky junction with the n-type region for adiode at the side walls 14B of each diode trench 14. Portions of themetal film 53 that form a schottky junction with the n-type region for adiode constitute schottky electrodes 70.

The conductive layer 30 is formed on the metal film 53, and covers theentire front surface (upper surface in FIG. 8) of the metal film 53. Theconductive layer 30 is electrically connected to correspondingelectrodes out of the plurality of external electrodes 2 mentioned above(see FIGS. 1 and 2). The gate electrodes 51 are connected to othercorresponding external electrodes 2 via not-shown relay wiring lines.

In the semiconductor device 1, in the transistor forming region D, theconductive layer 30, the metal film 53, the source electrodes 28, thebody regions 54, and the source regions 55 are electrically connected toeach other. Also, in the transistor forming region D, the rear electrode21, the semiconductor substrate 20, and a portion of the semiconductorlayer 22 where the body region 54 or the source region 55 is not formed(drain region 56) are electrically connected to each other.

This way, in the transistor forming region D, transistor cells 11A areconstructed individually. In the transistor cell 11A, a parasitic diodeis formed by the body region 54 and the drain region 56.

For example, in a state where the conductive layer 30 is grounded, and apositive voltage is applied to the rear electrode 21, a voltage equal toor greater than a threshold voltage is applied to the gate electrodes51. As a result, a channel is formed in each channel region X near theboundary between the body region 54 and the gate insulating film 50,allowing an electric current to flow from the rear electrode 21 towardthe conductive layer 30 via the channel.

In the diode forming region C, the rear electrode 21 forms an ohmiccontact with the semiconductor substrate 20, and the metal film 53 formsa schottky junction with the semiconductor layer 22 (n-type region for adiode), thereby constituting a schottky barrier diode 10. The schottkybarrier diode 10 and the transistor 11 are connected to each other inparallel. Also, in the diode forming region C, the p+ region 59 for adiode at the bottom surface 14A of each diode trench 14 forms a pnjunction with the n-type region for a diode, and with the pn junctionbetween the p+ region 59 for a diode and the n-type region for a diode,the above-mentioned pn diode 45 is constituted. As described above, inone diode trench 14, the pn diode 45 is formed at the bottom surface14A, and the schottky barrier diode 10 is formed at the side walls 14B.

In each diode trench 14 in the diode forming region C, the schottkybarrier diode 10 and the pn diode 45 are connected to each other inparallel. As described above, Vf of the schottky barrier diode 10 islower than Vf of the pn diode 45, and therefore, an electric currentflows through the schottky barrier diode 10 before the pn diode 45.

Also, as in the embodiment above (see FIG. 6), in a reverse bias state,a depletion layer 80 spreads from the pn diode 45 at the bottom of eachdiode trench 14, and respective depletion layers 80 at the bottom ofadjacent diode trenches 14 are connected to each other.

The configuration of the semiconductor device 1 of FIG. 6 may beappropriately applied to the semiconductor device 1 of FIG. 8, and insuch a case, it is possible to attain effects similar to those of thesemiconductor device 1 of FIG. 6.

FIG. 9 is a perspective view that schematically shows a semiconductorpackage according to an embodiment of the present invention.

As shown in FIG. 9, a semiconductor package 60 includes any one of theabove-mentioned semiconductor devices 1, a lead frame 61 made of ametal, and a resin package 65.

The semiconductor device 1 is bonded to the lead frame 61. The leadframe 61 includes a die pad 62 in a rectangular plate shape, leads 63Adisposed along one side of the die pad 62 with a gap therebetween, andleads 63B extending from another side of the die pad 62. The lead frame61 has a plurality of leads 63A and a plurality of leads 63B (four eachin this example).

In the semiconductor device 1, the rear electrode 21 (see FIGS. 6 and 8)is bonded to the upper surface of the die pad 62, and each lead 63A isconnected to a corresponding external electrode 2 on the surface of thesemiconductor device 1 through a bonding wire 64. This way, the leads63A and 63B are electrically connected to the schottky barrier diodes10, the pn diodes 45, and the transistors 11 in the semiconductor device1 (see FIGS. 1 and 2). In FIG. 9, the rightmost external electrode 2 isconnected to the gate electrode 24, and other external electrodes 2 areconnected to the source electrode 28 (see also FIG. 6). In this case,the rightmost lead 63A in FIG. 9 is a lead for the gate, and the otherthree leads 63A are leads for the source. All of the leads 63B are leadsfor the drain.

The semiconductor device 1 and the lead frame 61 bonded to each otherare covered by the resin package 65 such that the respective leads 63Aand leads 63B are exposed to the outside. The semiconductor package 60can be connected (mounted) to a mounting wiring substrate (not shown) byhaving the respective leads 63A and 63B face the mounting wiringsubstrate.

FIG. 10 is a circuit diagram of a DC-DC converter that uses thesemiconductor device of the present invention.

In a DC-DC converter 100 shown in FIG. 10, a control part (IC) 91 isconnected to a high side transistor 92 and a low side transistor 93, andthe semiconductor device 1 of the present invention can be used for thelow side transistor 93. In this case, the transistor 11 of thesemiconductor device 1 is used as the low side transistor 93, and theschottky barrier diode 10 connects the high side transistor 92 to thelow side transistor 93.

In addition to the above-mentioned, the present invention can beimplemented in various embodiments, and various design changes can bemade without departing from the scope specified by claims.

FIG. 11 is a diagram showing a modification example of the main part ofthe semiconductor device of FIG. 3.

Each of the diode trenches 14 described above extends as a straight lineover the entire region of the diode forming region C, for example (seeFIGS. 3 and 4), but as shown in FIG. 11, the diode trench 14 may bedivided into a plurality of parts on the same line extending along thesecond direction X. In this case also, as in the embodiment above, in aplan view, each diode trench 14 is formed in a rectangular shape that islonger in the second direction X. The source trenches 13 are formed in alinear shape along the first direction Y at the front surface 22A of thesemiconductor layer 22 as in the embodiment above, and two parallelsides (sides extending along the second direction X) H of each diodetrench 14 that is rectangular in a plan view are orthogonal to thelengthwise direction (first direction Y) of the source trench 13.

In the above embodiments, the pn diode 45 was formed at the bottomsurface 14A of each diode trench 14 (see FIGS. 6 and 8), but by omittingthe ion implantation on the diode trenches 14 (see FIG. 7I), theschottky barrier diode 10 may be formed not only at the side walls 14Bof the diode trench 14, but also at the bottom surface 14A.

In the above embodiments, the first conductive type was n-type, and thesecond conductive type was p-type, but conversely, the first conductivetype may be p-type, and the second conductive type may be n-type.

The thickness of the first interlayer insulating film 48A and thethickness of the second interlayer insulating film 48B may differ fromeach other. The depths of the gate trenches 12, the source trenches 13,and the diode trenches 14 may be changed appropriately. It is preferablethat the source trenches 13 and the diode trenches 14 be orthogonal toeach other in a plan view, but the intersection angle of these trenchesdoes not necessarily have to be 90°.

It will be apparent to those skilled in the art that variousmodification and variations can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover modifications and variationsthat come within the scope of the appended claims and their equivalents.In particular, it is explicitly contemplated that any part or whole ofany two or more of the embodiments and their modifications describedabove can be combined and regarded within the scope of the presentinvention.

What is claimed is:
 1. A semiconductor device, having: a semiconductorlayer of a first conductive type; a body region of a second conductivetype formed in the semiconductor layer; a source region and a drainregion of the first conductive type formed in the semiconductor layer soas to be separated from each other across the body region; a sourcetrench formed in the semiconductor layer, the source trench penetratingthe source region and reaching the body region; a body contact regionformed near a bottom of the source trench and in the semiconductor layerof the first conductive type that includes the body region, the bodycontact region being the second conductive type and having a higherimpurity concentration than that of the body region; a source electrodeembedded in the source trench; a gate electrode facing through a gateinsulating layer the body region that lies between the source region andthe drain region; a first conductive type region for a diode formed inthe semiconductor layer; a diode trench formed in the semiconductorlayer that includes the first conductive type region for a diode; and aschottky electrode forming a schottky junction with the first conductivetype region for a diode at inner walls of the diode trench.
 2. Thesemiconductor device according to claim 1, wherein the diode trench hasthe same depth as that of the source trench.
 3. The semiconductor deviceaccording to claim 1, further having: a first interlayer insulating filmthat insulates the gate electrode and the source electrode from eachother; and a second interlayer insulating film disposed between theschottky electrode and a surface of the first conductive type region fora diode outside of the diode trench.
 4. The semiconductor deviceaccording to claim 3, wherein the first interlayer insulating film andthe second interlayer insulating film have the same thickness.
 5. Thesemiconductor device according to claim 3, wherein the schottkyelectrode has a first thickness at the inner walls of the diode trench,and a second thickness that is greater than the first thickness on thesecond interlayer insulating film.
 6. The semiconductor device accordingto claim 1, wherein a plurality of said diode trenches are arranged witha gap therebetween.
 7. The semiconductor device according to claim 1,wherein the source electrode and the schottky electrode are made of thesame electrode material.
 8. The semiconductor device according to claim1, wherein the source trench is formed at a surface of the semiconductorlayer in a linear shape along a first direction, and wherein the diodetrench is formed at the surface of the semiconductor layer in a linearshape along a second direction that is orthogonal to the firstdirection.
 9. The semiconductor device according to claim 1, wherein thediode trench is rectangular in a plan view.
 10. The semiconductor deviceaccording to claim 9, wherein the source trench is formed at a surfaceof the semiconductor layer in a linear shape, and wherein two parallelsides of the diode trench that is rectangular in a plan view areorthogonal to a lengthwise direction of the source trench.
 11. Thesemiconductor device according to claim 1, wherein the source region andthe drain region are disposed so as to be separated from each otheracross the body region along a thickness direction of the semiconductorlayer, wherein the semiconductor device further has a gate trench thatreaches the drain region, penetrating the source region and the bodyregion, and wherein the gate electrode is embedded in the gate trench.12. The semiconductor device according to claim 11, wherein the diodetrench is formed shallower than the gate trench.
 13. The semiconductordevice according to claim 1, wherein the source region and the drainregion are arranged along a surface of the semiconductor layer with agap therebetween.
 14. The semiconductor device according to claim 1,further comprising a second conductive type region for a diode formed inthe first conductive type region for a diode so as to be in contact witha bottom of the diode trench, the second conductive type region for adiode forming a pn junction with the first conductive type region for adiode.
 15. The semiconductor device according to claim 14, wherein aplurality of said diode trenches are arranged with a gap therebetween.16. The semiconductor device according to claim 15, wherein the gapbetween the plurality of diode trenches is set such that a depletionlayer spreading from each said pn junction is connected to one anotherin a reverse bias state.
 17. The semiconductor device according to claim14, wherein the schottky electrode includes a schottky/ohmic electrodelayer that forms a schottky contact with the first conductive typeregion for a diode at the inner walls of the diode trench and that formsan ohmic contact with the second conductive type region for a diode atthe bottom of the diode trench.